The present invention relates to a stereoscopic landform display apparatus for displaying landform stereoscopically based on landform data, and more particularly, to a stereoscopic landform display apparatus capable of automatically determining an altitude value to be displayed in accordance with asperity exhibiting concavities and convexities of ground.
Conventionally, there is reported an example for displaying a stereoscopic landform as shown in FIGS. 19 and 20 by a stereoscopic landform display apparatus which displays the map while uniformly changing and emphasizing the altitude value in accordance with an altitude magnification input by a user.
However, according to such a conventional stereoscopic landform display apparatus, even in relatively flat urban area or relatively steep-sided mountainous area, for example, since the landform is displayed at the same altitude magnification uniformly, when it is desired to emphasize the difference in altitude in urban area, or when it is unnecessary to emphasize and display at altitude magnification in mountainous area to the contrary, there are problems that it is necessary for a user to determine an appropriate altitude magnification each time by himself or herself, and the input operation of the altitude magnification is troublesome.
The present invention has been accomplished in view of such circumstances, and it is an object of the invention to provide a stereoscopic landform display apparatus capable of displaying an easy-to-see stereoscopic landform image in accordance with landform state of a display subject region.
A stereoscopic landform display apparatus according to the present invention comprises, landform data storing means for storing landform data including altitude value of a landform, display region designating means for designating a display subject region to be displayed, computation means which reads the landform data designated by the display subject region from the landform data storing means, obtains altitude magnification for emphasizing and displaying an undulation state of the landform based on the landform data within this region, and performs a computation of a stereoscopic landform image from the altitude value which is multiplied by this altitude magnification, and image display means for displaying the stereoscopic landform image.
With this structure, the landform data comprising altitude value of landform are stored, and when a display subject region to be displayed is designated, landform data designated by this display subject region are read, altitude magnification for emphasizing and displaying undulation state is obtained based on landform data in this region, a computation of a stereoscopic landform image is performed from an altitude value which is multiplied by this altitude magnification, and this stereoscopic landform image is displayed. Therefore, it is possible to display easy-to-see stereoscopic landform image in accordance with a state of landform in the display subject region. As a result, it is possible to automatically determine the altitude magnification such that when the landform is flat, asperity of the landform is emphasized, and when the landform is steep, the asperity of the landform is not emphasized.
It is preferable that the computation means comprises, reference altitude value determining means which reads, from the landform data storing means, landform data in a range covering the display subject region, and determines altitude value of a reference point displayed in display subject region based on this landform data, actual asperity value determining means for determining an actual asperity value indicative of undulation state of the landform based on the read landform data, altitude magnification determining means for determining the altitude magnification in the display subject region based on this actual asperity value, display altitude value generating means for generating display altitude value by multiplying each of the altitude values forming the read landform data by this altitude magnification, display data generating means for generating landform display graphic data which are required for displaying the landform based on this display altitude value, coordinate conversion means for coordinate converting this landform display graphic data to a stereoscopic landform image, and drawing means for drawing this stereoscopic landform image on the image display means.
With this structure, landform data in a range covering the display subject region are read, and altitude value of the reference point displayed in display subject region is determined based on this landform data. Next, the actual asperity value indicative of undulation state of the landform is determined based on the read landform data, the altitude magnification in the display subject region is determined based on this actual asperity value. Next, the display altitude value is generated by multiplying each of the altitude values forming the read landform data by this altitude magnification, and landform display graphic data which are required for displaying the landform are generated based on this display altitude value. Then, this landform display graphic data is coordinate converted into the stereoscopic landform image. Therefore, it is possible to automatically determine the altitude magnification such that when the landform is flat, asperity of the landform is emphasized, and when the landform is steep, the asperity of the landform is not emphasized.
It is preferable that the actual asperity value determining means determines the actual asperity value using landform data within a region previously defined in the vicinity of the display reference point.
With this structure, the actual asperity value is determined using landform data within a region previously defined in the vicinity of the display reference point. Therefore, in a bird""s eye view for example, it is possible to ignore the landform data information whose influence on a direct display result such as a region far from a visual point displayed while compressed is expected to be small. As a result, it is possible to reduce the calculation amount to relatively small value.
It is preferable that the altitude magnification determining means includes input means for inputting a value for designating altitude magnification, and determines a quotient obtained by dividing this input value input by the actual asperity value, as the altitude magnification.
With this structure, the value for designating altitude magnification is input, and the quotient obtained by dividing this input value input by the actual asperity value is determined as the altitude magnification. Therefore, it is possible to display in accordance with a user""s taste using elevation which is a relatively easy index. It is possible to avoid an operational troublesome that the user must frequently reset the altitude magnification.
Further, it is preferable that the altitude magnification determining means determines the altitude magnification such that it becomes equal to a predetermined value or greater.
With this structure, since the altitude magnification is determined such that it becomes equal to a predetermined value or greater, when the altitude magnification becomes small even through the actual asperity value is great for example, it is possible to prevent the landform from being displayed flatly as compared with the actual landform by defining the lower value of the altitude magnification value as described above.
It is preferable that the drawing processing means visually draws a shape indicative of degree of the altitude magnification independently from drawing of the stereoscopic landform image.
With this structure, since the drawing means visually draws a shape indicative of degree of the altitude magnification independently from drawing of the stereoscopic landform image, it is possible to estimate the original asperity state intuitively from the display screen.
Further, it is preferable that the landform data storing means stores map data including map elements including at least roads and place names, in addition to the landform data; the display region designating means reads the map element designated by the display subject region from the landform data storing means together with the landform data; the display data generating means generates display graphic data also with respect to the map element which is read; the coordinate conversion means carries out coordinate conversion also for the display graphic data; and the drawing processing means draws the display graphic data which is coordinate converted together with the landform display graphic data.
With this structure, the map data including map elements including at least roads and place names are stored, in addition to the landform data, the map element designated by the display subject region is read from the landform data storing means together with the landform data, the display graphic data are made also with respect to the read map element. Next, coordinate conversion is carried out also for this display graphic data, and the display graphic data which is coordinate converted is drawn. Therefore, it is possible to also display the map elements on the stereoscopic landform image and for example, it is possible to display the stereoscopic landform image and the map element and to use for guiding roads as a navigator.
Further, it is preferable that the computation means comprises, reference altitude value determining means which reads, from the landform data storing means, landform data in a range covering the display subject region, and determines altitude value of a reference point displayed in display subject region based on this landform data, actual asperity value determining means for determining an actual asperity value indicative of undulation state of the landform based on the read landform data, altitude magnification determining means for determining the altitude magnification in the display subject region based on this actual asperity value, display altitude value generating means for generating display altitude value by multiplying each of the altitude values forming the read landform data by this altitude magnification, landform display color determining means for determining display color of the landform based on this display altitude value, display data generating means for generating landform display graphic data which are required for displaying the landform based on this display altitude value or altitude value, coordinate conversion means for coordinate converting this landform display graphic data to a stereoscopic landform image, and drawing means for drawing this stereoscopic landform image on the image display means using this landform display color.
With this structure, the landform data in a range covering the display subject region is read, and the altitude value of a reference point displayed in display subject region is determined based on this landform data. Next, the actual asperity value indicative of undulation state of the landform is determined based on the read landform data, and the altitude magnification in the display subject region is determined based on this actual asperity value. Then, the display altitude value is generated by multiplying each of the altitude values forming the read landform data by this altitude magnification, and the display color of the landform is determined based on this display altitude value. Then, the landform display graphic data which are required for displaying the landform are made based on this display altitude value or altitude value, and this landform display graphic data is coordinate converted into a stereoscopic landform image, and this stereoscopic landform image is drawn using this landform display color. Therefore, even in a relatively flat landform, its asperity is emphasized by display color, and the stereoscopic shape can easily be seen. Further, when the shape is not emphasized and only the display color is emphasized, it is possible to see the information of altitude change by the change of display color, and to avoid a display manner that a high place near the current place obstructs a user""s view and as a result, it is possible to secure a line-of-sight up to far place.
Further, it is preferable that the actual asperity value determining means broadens up to landform data possessed by a region which is not displayed around the display subject region, and refers to the broadened landform data, thereby determining the actual asperity value.
With this structure, the actual asperity value determining means broadens up to landform data possessed by a region which is not displayed around the display subject region, and refers to the broadened landform data, thereby determining the actual asperity value and therefore, by increasing the number of broadened landform data, even if the display region moves with time as the visual point moves, a reading amount G of landform data to be displayed is reduced relatively and as a result, the variation of the altitude magnification is smoothened gently, and it is possible to display the easy-to-see image.
Further, it is preferable that the actual asperity value determining means broadens landform data to be referred along an expectable traveling direction, thereby determining the actual asperity value.
With this structure, the actual asperity value determining means broadens landform data to be referred along an expectable traveling direction, thereby determining the actual asperity value and therefore, the altitude magnification is determined on the assumption that the landform data are selected in accordance with the moving direction of the visual point which is broadened along the traveling direction, a reading amount G of landform data to be displayed is reduced relatively and as a result, the variation of the altitude magnification is smoothened gently, and it is possible to display the easy-to-see image.
Further, it is preferable that the altitude magnification determining means determines the altitude magnification using altitude value at the display reference point, in addition to the actual asperity value.
With this structure, the altitude magnification determining means determines the altitude magnification using altitude value at the display reference point, in addition to the actual asperity value, even if the same actual asperity value is obtained, it is possible to automatically set the magnification which differs in accordance with difference in height of the position of the vehicle (display reference point), and for example, it is possible to control the magnification such that when the vehicle is in a low place in the altitude distribution in the entire display region, the magnification is suppressed to a low value, and when the vehicle is in a place of intermediate height, the magnification is emphasized.
Further, it is preferable that the altitude magnification determining means determines the altitude magnification by referring also to altitude magnification which was determined in the past.
With this structure, the altitude magnification determining means determines the altitude magnification by referring also to altitude magnification which was determined in the past and therefore, the variation of the altitude magnification with time is smoothened gently, and it is possible to display the easy-to-see image.
Further, it is preferable that the altitude magnification determining means determines the altitude magnification such that it becomes equal to a predetermined value or less.
With this structure, since the altitude magnification is determined such that it becomes equal to a predetermined value or less, it is possible to prevent the altitude magnification from being emphasized excessively and as a result, it is possible to display the easy-to-see stereoscopic landform image.
Further, it is preferable that the landform display color determining means determines a display color corresponding to a predetermined lower limit value instead of this display altitude value when the display altitude value becomes extremely small, and determines a display color corresponding to a predetermined upper limit value instead of this display altitude value when the display altitude value becomes extremely great.
With this structure, the display color corresponding to a predetermined lower limit value is determined instead of this display altitude value when the display altitude value becomes extremely small, and the display color corresponding to a predetermined upper limit value is determined instead of this display altitude value when the display altitude value becomes extremely great and therefore, it is possible to define the table in which the display altitude values and display colors are corresponding to one another within a relatively small range, and it is possible to reduce the number of necessary colors.